I train the good morning and the stiff-leg deadlift with completely different modalities. I find that the stiff-leg deads were something I could push the loading on, but I kept the good mornings light and focused on the stretch. No other lift built my posterior chain like hstiff-leg deads from a 4-inch deficit.
From the upper back to erectors to hamstrings, this was my "go to" for total posterior chain smashing. I eventually worked up to over 600 pounds for reps on these.
With good mornings (shown here) I kept the loading in the 185-225 pound range, even when my deadlift was consistently over 700. That's the contrast in how you should be approaching loading if you choose to include these two lifts as part of your deadlift program.